1. Field of the Invention
The present invention relates to an automatic inspection apparatus for generator turbines and, more particularly, to an automatic inspection apparatus for generator turbines and a system using the same, which may eliminate disturbance due to vibration by stabilizing contact pressure of a probe to an inspection object to enhance inspection reliability, and which has a light weight to be easily installed or removed.
2. Description of the Related Art
In general, generating facilities have a turbine 1 that drives a generator using high temperature and pressure vapor from a nuclear reactor or boiler to generate electricity, as schematically shown in FIG. 1. The turbine 1 includes a rotor 2, which includes a plurality of discs 3 arranged at predetermined intervals, and blades 4 having different diameters from one another and coupled to the discs 3, respectively. Thus, a vapor having high temperature and high pressure is introduced to collide with and rotate the blades 4, so that the rotor 2 can be rotated to generate electricity through a generator (not shown).
However, since the blades 4 of the turbine 1 are directly exposed to the high temperature and pressure vapor and are subjected to both vibration and centrifugal force, a root 5 at which the blade 4 is fastened to the disc 3 is likely to suffer from cracking. Accordingly, it is necessary to perform periodic inspection of the turbine 1 during operation of the generating facilities or in an inspection term. In particular, it is necessary for the root 5 to be subjected to thorough inspection.
Generally, a nondestructive testing method employing ultrasound waves is employed to inspect the turbine 1. However, the complex structure of the turbine 1 makes it difficult to perform general automatic inspection. Therefore, manual inspection is usually applied to the turbine 1. During manual inspection, a worker evaluates a signal generated when an ultrasound probe is brought into contact with the root 5 of the blade 4. However, the accuracy and reliability of the manual inspection are low because inspection must be performed within a small and narrow space and there are several hundred blades 4 within the turbine 1 to be inspected. Accordingly, a variety of methods and apparatuses for automatic inspection have been developed.
One example of the apparatus for automatic inspection includes an inspection apparatus 10 as shown in FIG. 2. The inspection apparatus 10 employs ultrasound waves for inspecting the roots (not shown) of the blades 12 in the turbine 11 and performs inspection while moving along a rail 13 disposed in a longitudinal direction of the turbine 11 or in a state of being attached to a body of the turbine 11.
Specifically, the turbine 11 to be inspected is retracted from a turbine casing (not shown) and both ends of the rotor 14 are seated on a stand 15. On the rail 13, the inspection apparatus 10 moves to a position for inspection. Then, the root is inspected using a probe (not shown) mounted on a leading end of an arm 16 while rotating the turbine 11 360 degrees with respect to the stand 15.
Due to a very small gap between one root and another adjacent root of the circumferentially arranged blades 12, this inspection method causes vibration when the turbine 11 rotates. The vibration may cause insufficient contact between the probe and an inspection object, i.e. the root.
Further, the arm 16 is too long to enhance contact of the probe or to achieve satisfactory contact, thereby making it difficult to obtain accurate ultrasound signals and necessitating additional inspection.
In addition, since the inspection apparatus 10 needs to be relatively heavy in order to stably support the long arm 16, there is a need to improve installation and maintenance of the excessively heavy inspection apparatus 10.
A variety of automatic inspection apparatuses are known in the art. For example, Korean Utility Model No. 20-270825, filed on Mar. 23, 2002, discloses a probe device, entitled “Probe device for Nondestructive Inspection of Blade Root of Steam Turbine in Power Plant.” In this device, a holder body supporting a probe is connected to an inspection apparatus magnetically attached to a turbine and the probe is movable upward, downward, forward and backward through the holder body.
Korean Patent Laid-open Publication No. 2006-0008552, filed on Jan. 27, 2006, discloses an inspection apparatus, entitled “Nondestructive Inspection Apparatus for Turbine Blade Root in Power Plant.” This apparatus performs inspection by fixing a probe to the blade without retracting the turbine from the casing. That is, the blade is inspected by adjusting the height and rotation of the probe through a plurality of joints.
Korean Patent Laid-open Publication No. 2007-0013007, filed on 30 Jan. 2007, discloses an apparatus and method for inspection, entitled “Apparatus and method using a multi joint robot for automatic ultrasonic inspection of a steam turbine in a power plant.” In this apparatus, the multi-joint robot is provided with an ultrasonic sensor at a leading end of an arm, and inspects the front and back of the blade while moving along control traces of a controller. However, the apparatus does not have a traveling function.
U.S. Pat. No. 7,075,296, filed on 11 Jul. 2006, discloses an apparatus, entitled “Inspection carriage for a turbine blade.” This inspection carriage inspects the front and back of the blade while using a motor to drive forward and backward movement and rotation of an ultrasound probe, but the apparatus itself is not capable of motion.
U.S. Patent Publication No. 2009/0126493, filed on May 21, 2009, discloses an apparatus, entitled “Nondestructive inspection head for parts having a limited enveloping space.” The inspection head is controlled by an independent driver and performs inspection while freely moving and rotating between blades using multiple shafts.
However, reliability and efficiency of the conventional automatic inspection apparatuses are limited due to vibration occurring between a part to be inspected and the probe or it is difficult to maintain constant contact pressure of the probe. Further, the inspection apparatuses are so heavy that installation and removal of such apparatuses require a hoisting device or take too much time and labor.